In a magnetic rotation-angle detectors, there is a method of mounting a magnetic body slit, formed by machining a disk-shaped magnetic body such that it has a slit shape, on a motor and then using a magnetic sensor to detect a change in a magnetic field as the magnetic body slit rotates.
Patent Literature 1 describes a technique in which, in a magnetic encoder, a detection body is arranged between a magnetic-body slit plate and a plate magnet, and a plurality of magnetic resistance elements are arranged on the circumference of the detection body, which has a diameter substantially equal to that of the magnetic-body slit plate. According to Patent Literature 1 , it is assumed that, because magnetic resistance elements are arranged over the entire circumference of a magnetic-body slit plate, the rotation of the magnetic-body slit plate can be detected while shaft flexures and mounting errors of the rotation parts are cancelled out.